Preventing & Dealing with Fish Health Problems

1. Cleaning biological filter media with tap water: tap water contains chlorine that will kill off the nitrifying bacteria which live in the filter.This will result in a build up of ammonia and nitrite. Biological media should be rinsed in a bucket of pond water.
2. Over-feeding: Feeding your fish too much will result in excessive levels of solid waste being produced.This will lead to deteriorating water quality and the encouragement of disease causing organisms. Fish should be fed no more than three to four times a day, feeding no more than they can consume within a few minutes (see the ‘Feeding your Pond Fish’ leaflet).
3. Build up of Silt: If silt is allowed to accumulate, it will provide an environment in which certain disease causing organisms will thrive. It will also lead to increased levels of pollutants and a decrease in oxygen levels.This can be prevented through the regular use of a pond vacuum, or by using a solids-handling pump, such as the TetraPond OFX.
4. Over-stocking: If you have too many fish in the pond, the filter will have a harder time maintaining good water quality.There may also not be enough oxygen in a heavily stocked pond, in which case an air-pump, or extra fountain should be added. Physical damage is also more common in over-stocked ponds and the levels of stress tend to be higher as well. If your pond is too heavily stocked then you will either have to remove some of the fish or upgrade the equipment.
5. Damaging objects: If your pond contains a lot of sharp objects then there is a danger that the fish will damage themselves on them.This often occurs when the fishes are startled and they dart to safety, knocking into things in their panic. Physical damage caused in this way can quickly lead to infection and therefore, if possible, the offending items should be removed from the pond.
6. Not conditioning tap water: When adding tap water to the pond it should always be conditioned with TetraPond WaterSafe in order to neutralise its harmful chlorine and heavy metal content. Failure to do this will result in damage to the fish’s gills, ultimately leading to health problems.
7. Turning off the filter for too long during the winter: Ideally, the filter should be left running all winter in order to maintain a low level of nitrifying bacteria. If you do need to turn it off, then make sure it is turned back on well in time for the spring. Failure to do this will result in a build up of ammonia and nitrite during the early part of the year.
8. Failure to refresh the water: Every so often it is a good idea to carry out a partial water change in the pond, in order to replace some of the essential elements that are used up by various natural processes. Replacing 25% of the water with conditioned tap water is normally sufficient to do this. Failing to do this can sometimes result in health problems and a drop in the efficiency of the filter.
9. Not protecting the pond from predators: Fish predators, in particular herons, can cause physical damage to fish which can then leave them open to infection. If there are herons or other predators in your area, then the pond should be protected with a net, or suitable anti-heron device. (See Protecting your Pond from Predators leaflet.)
10. Turning off fountains and waterfalls at night: Fountains and waterfalls should be left on 24hrs a day during warmer weather, as it is at night when oxygen can fall to critical levels.This is because at night, plants and algae stop producing oxygen, yet they continue to use it up.

Fungal infections often arise at the site of any physical damage sustained by the fish.They can also occur as “secondary infections” at sites where there is an existing infection (for instance around ulcers). Fungus is present at low levels in the pond all of the time, and it is only when the fish is stressed or damaged that it tends to cause a problem.

Parasitic infections are those caused by parasites. Parasites come in a variety of shapes and forms, and it is usually necessary to examine them under a microscope in order to identify them.There are some common parasites that are easier to identify, for example white spot (Ichthyophthirius multifiliis) appears as small white dots over the skin and fins. Ponds that are very crowded with poor water quality are most at risk from parasite problems.

Bacterial infections are caused by a range of different bacteria species.They tend to be encouraged when the fish is stressed and where the pond is dirty. Often when fish become ill with no obvious symptoms, bacteria are to blame. They may infect the fish externally resulting in symptoms that are reasonably obvious, or they may cause internal infections. Internal infections are not only difficult to diagnose, but also difficult to treat, as they usually require prescription anti-biotics.